From an exhibit I went to last year... Fashioning Fashion: European Dress in Detail, 1700-1915 at the LACMA.

During the early 18th century, Emma’s time period, the most typical style of dress was the empire silhouette (Above: far right) which entailed a closely fitted torso just under the chest and a loose falling skirt below. Women of Emma’s position even had rules of etiquette for which dress to wear at a particular time of day. Morning dresses, worn inside the house, were high-necked and long-sleeved and devoid of superfluous decoration. Evening gowns such as the one above were low cut, often extravagantly trimmed and decorated with lace and ribbons. A lady of distinction such as Emma would often advise young ladies, like Harriet, to wear softer shades of color, such as pinks, periwinkle blue, or lilacs. The more dignified woman could wear fuller colors, such as purple, black, crimson, deep blue, or yellow.